Process for the manufacture of fibers and filaments of polyethylene terephthalate



Patented Apr. 12, 1966 3 245,955 PROCESS FOR THE MANUFACTURE OF FEBERSAND FILAMENTS F POLYETHYLENE TEREPH. THALATE Martin Richer, Kronberg,Taunus, Germany, asslgnor to Farbwerke Hoechst Aktiengeseilschattvormals Meister Lucius & Bruning, Frankfurt am Main, Germany, acorporation of Germany No Drawing. Filed Sept. 12, 1961, Ser. No.137,508 Claims priority, application Germany, Sept. 14, 1960, F 32,112 8Claims. (Cl. 260-75) The object of the present invention is a processfor the manufacture of fibers and filaments of polyethylenetercphthalate. It is a further object of the invention to manufacturefibers and filaments of polyethylene terephthalate which have littletendency towards pilling.

Great difficulties are encountered with textile structures containingsynthetic fiber material owing to the fact that these structures,especially dress-materials, have a strong tendency towards pilling. Bypilling there is understood the phenomenon that when textile structuresare rubbed against one another or against another structure smallconglomerations of individual fibers are forming which appear in theform of little knots on the surface and can be removed with difiicultyonly. Several proposals have been made in order to remedy this evil. Ithas been proposed, for example, to singe and/ or to brush and to shearwoven fabrics of synthetic filaments in order to reduce the pillingeffect. These processes, however, involve additional expensiveoperations in which, moreover, the fabrics may be tendered by the heatrequired for singeing.

It has also been proposed to subject synthetic fibers or yarns of whichwoven fabrics are to be made to a chemical after-treatment in order toreduce the later pilling effect. Thus it is known, for example, to treatpolyethylene terephthalate fiber yarns with aqueous solutions ofhydrazine hydrate or ethylene diamine. This process has thedisadvantage, however, that the yarns are frequently tendered in aconsiderable degree. Moreover, the fastness to light and resistance toheat of the synthetic fibers are very detrimentally affected in suchoperations. Attempts to reduce the later tendency towards pilling bymodifying the manufacturing procedure of the synthetic fibers such, forexample, as altering the stretch during the spinning procedure or thestretching ratio, have not led to satisfactory results either.

Now I have found a process for the manufacture of fibers of polyethyleneterephthalate that have little tendency towards pilling which consistsin adding to the polyethylene terephthalate 0.01 to of its weight ofterephthalic acid, isophthalic acid, dimethylterephthalate, dimethylisophthalate, diglycol terephthalate, diglycol isophthalate, or amixture of these substances as a decomposing agent and working up theproduct obtained into filaments according to the melt extrusion processin known manner, the filaments thus obtained having a specific viscositywhich is by 0.2 to 0.5 units lower than that of the originalpolyethylene terephthalate. The specific viscosity is determined bydissolving the polyethylene terephthalate in a mixture composed of 60parts of phenol and 40 parts of tetrachloroethane to give a 1% solutionand measuring the viscosity in a capillary viscosimeter at 25 C. Sinceportions of low molecular weight are contained in almost any polymer, itcould not be foreseen in which way the addition of the aforementionedproducts would affect the properties of the polyethylene terephthalateand the filaments made thereof. It was surprising, therefore, that byadding the said substances there can be attained a very uniformdecomposition of the polyethylene terephthalate in such a manner that,by adding definite proportions by weight of monomer, the specificviscosity of the polyethylene terephthalate formed can be reduced andprecisely adjusted. When carrying out the process of the presentinvention for the manufacture of filaments having a poor tendencytowards pilling, it was found that there is not obtained a mixture ofthe individual decomposing agents with the polyethylene terephthalatebut that a chemical reaction takes place (decomposition of the chainmolecules), whereby the physical properties of the filaments aremodified and especially the tendency towards pilling is largelyabolished.

I have found, moreover, that the amount of the decomposing agent addedmust be limited and exactly dosed since by the addition of too greatamounts of decomposing agents to the polyethylene terephthalate prior tothe spinning process the various physical data of the filaments areadversely affected; thus, for example, the tensile strength of thefilaments is strongly reduced if too great a quantity of decomposingagent is applied whereby the filaments obtained become brittle.

The decomposing agent can be incorporated according to various methods:

1) After the termination of the polycondensation, i.e. after themanufacture of the polyethylene terephthalate which can take placecontinuously or discontinuously, the desired amount of decomposing agentis added to the molten polyethylene terephthalate. In this procedure,the melt of polyethylene terephthalate is advantageously kept under anatmosphere of nitrogen of atmospheric pressure and the decomposing agentis slowly added, with agitation. After the addition of the decomposingagent, stirring is continued for 5 to 15 minutes. By the addition of thedecomposing agent and depending on the amount applied thereof, theviscosity of the melt of polyethylene terephthalate is reduced to agreater or lesser extent. The polyethylene terephthalate obtained caneither be fed in the molten state directly to the spinning head, forexample with the aid of a screw conveyer, and there be spun intofilaments, or the melt is forced through a slot die and cooled in theair or in water. The ribbon obtained is then worked up into granules ina cutting machine. These granules can be stored and transported. Fromthese polyethylene terephthalate granules there are obtained filamentswhen, after drying the granules to a water content of less than 0.04%,they are melted again and the melt is forced through a spinneret bymeans of spinning pumps and the filaments obtained are taken off.

(2) It is likewise possible to add the decomposing agent to thepolyethylene terephthalate in the following manner:

The melt of polyethylene terephthalate obtained after thepolycondensation is formed into ribbons and these are worked up intogranule-s in a cutting machine. These granules are mixed with thedesired amount of the decomposing agent which should preferably be inthe pulverulent or granular state. In order to warrant that the granulesare intimately mixed with the decomposing agent, it is necessary to mixthe composition for several hours, for example in an offset tumblingmixer. It is advantageous to add the decomposing agent to the granulesprior to drying the granules and then to dry the mixture to a watercontent of less than 0.04% of its weight. In the drying process thepulverulent or granular decomposing agent is bonded to the granules sothat in the further processing of the mixture a uniform distribution ofthe decomposing agent in the granules is warranted. In the furtherprocessing procedure the mixture is melted, in the course of whichprocedure the decomposing agent is dissolved in the melt of thepolytageous to use as highly a concentrated solution as possible. Thissolution is added to the polyethylene terephthalate obtained after thepolycondensation which, after extrusion into ribbons and comminution, isavailable in grandular form, while the desired amount of the decomposingagent has to be metered in carefully. The solution of the decomposingagent must be well mixed with the granular product. It is suitable forthis purpose to mix the composition for several hours, for example in anoffset tumbling mixer. When intimate mixing has been attained, thesolvent is gradually evaporated. This can either be done by creating avacuum or by slowly heating the composition to a temperature situated afew degrees above the boiling point of the solvent. When the solvent isevaporated, the decomposing agent deposits in a finely distributedformon the surface of the granular product. The granules thus obtainedare dried to a water content'of' less than 0.04% by weight. Owing to theuniform deposition of the decomposing agent on the granular product, theuniform distribution is warranted even 'in the case of a furtherprocessing. The granules are melted while the decomposing agent isdissolved in the melt of the polyethylene terephthalate and thepolyethylene terephthalate decomposes to the desired extent. The meltobtained has a lower viscosity than the melt of the originalpolyethylene terephthalate. With the aid of spinning pumps the melt isforced through a spinneret and shaped into filaments that can besubjected to a further treatment in known manner.

The following examples serve to illustrate the invention but they arenot intended to limit it thereto:

Example 1 1 kg. of polyethylene terephthalate granules (specificviscosity: 0.85) were prepared from terephthalic acid and ethyleneglycol in known manner and mixed with grams of a granulartransesterification product of dimethyl terphthalate and glycol (meltingpoint: 150 to 160 C.), then dried for two hours at 180 C. and spun at290 C. in a melt spinning installation through a spinneret having 200holes. After spinning the polyethylene terephthalate had a specificviscosity of 0.55. The melting point of the polyethylene terephthalatewas not noticeably reduced by the spinning process (melting point: 250C.). Then the filaments were heated and stretched in the ratio of1:3.65, crimped, prepared, subjected to heat setting and cut. The normalpolyethylene terephthalate fibers had a tensilev strength of 3.8 gramsper denier and an elongation at break of while the fibers preparedaccording to the process of the present invention had a tensile strengthof 3.4 grams per denier and an elongation at break of 23%. The yarns(No. 48 double/500 twists S/500 twists Z) which were spun from thestaple fibers prepared according to this example had a considerablylower pilling efiect than normal polyethylene terephthalate yarns.

Example 2 1 kg. of granulated polyethylene terephthalate was prepared asdescribed in Example 1 and mixed with 10 g. of dimethyl terephthalate.After drying, the mixture was spun into filaments in a melt spinninginstallation. The filaments. had a specific'vi cosity of 0.57 and ameltin point of about 258 C. They were stretched as described in Example1 and processed into staple fibers. The tensile strength of normalpolyethylene terephthalate fibers is 3.8 grams per denier with anelongation at break of 25 Fibers prepared according to this example hada tensile strength of 3.3 grams per denier and an elongation at break of22%. The yarns (No. 40 double/400 twists 8/450 twists Z), which werespun from the staple fibers prepared according to this example, had anappreciably lower tendency towards pilling.

Example 3 10 grams of dimethyl terephthalate were dissolved in cc. ofacetic acid ethyl ester and 1 kg. of granulated polyethyleneterephthalate was added to this solution. Then the acetic ester wasevaporated in vacuo, the lacquered granules were dried and processedaccording to the melt extrusion process intofibers as described inExample 2. The yarns obtained possessed the same properties as thoseobtained according to Example 2.

Example 4 30 grams of diglycol terephthalate were dissolved in Example 5200 kg. of polyethylene terephthalate were prepared in a vessel(capacity: 500 kg.) by transesterification from dimethyl terephthalateand ethylene glycol and subsequent condensation, as usual. As soon asthe condensation mass had attained a specific viscosity of 0.85, 1 kg.of diglycol terephthalate (preliminary condensate) was charged to thecondensation vessel in small portions without vacuum, under anatmosphere of nitrogen, while agitation was continued for 15 minutes at280 C. Then the molten contents of the vessel were discharbed and themelt granulated in the usual manner. The granules had a specificviscosity of 0.6. The polyethylene terephthalate filaments preparedtherefrom in a melt spinning installation were processed into staplefibers as described in Example 1. The filaments had a tensile strengthof 3.5 grams per denier. From the staple fibers there was obtained ayarn (No. 48 double/500 twists S/500 twists Z) which had a very lowtendency towards pilling.

I claim:

1. A process for manufacturing polyethylene terephthalate fibrousstructures having improved wearing prop erties which comprises admixingpolyethylene terephthalate having a specific viscosity of about 0.8 toabout 0.9 with 0.1 to 5% by weight, calculated on the weight of saidpolyethylene terephthalate, of a decomposing agent selected from thegroup consisting of dimethyl terephthalate, dimethyl isophthalate,diglycol terephthalate and diglycol isophthalate, reacting said mixtureto decompose said polyethylene terephthalate to a specific viscosity ofabout 0.5 to about 0.6, and spinning said mixture to form said fibrousstructures, said specific viscosity being determined by measuring theviscosity of a 1% solution of said polyethylene terephthalate in amixture of 60 parts phenol and 40 parts tetrachloretha'ne in a capillaryviscosimeter at 25 C.

2. A process as defined in claim 1 wherein said fibrous structures aremultifilamcnts.

3. A process as defined in claim 1 wherein said fibrous structures aremonofilaments.

4. A process as defined in claim 1 wherein said polyethyleneterephthalate is in molten form and said decomposing agent is admixedtherewith.

5. A process as defined in claim 1 wherein said polyethyleneterephthalate is dried after admixture of said decomposing agent andprior to spinning.

6. A process as defined in claim 1 wherein said polyethyleneterephthalate is in granular form and said step of admixing saidpolyethylene terephthalate and said decomposing agent, prior to reactingthem, comprises dissolving said decomposing agent in a solvent selectedfrom the group consisting of methylene chloride, dioxane, acetic acidethyl ester and ethanol, applying the solution of said decomposing agentand said solvent to said polyethylene terephthalate granules,evaporating said solvent from said granules, and drying said granules.

7. A process as defined in claim 1 wherein said mixture of polyethyleneterephthalate and decomposing agent is reacted at a temperature in therange of about 270 to 290 C. and continuously stirred for about 5 to 15minutes.

8. In a process for manufacturing fibrous structures of polyethyleneterephthalate, the step of improving the wearing properties of saidfibrous structures which comprises admixing with polyethyleneterephthalate having a specific viscosity of about 0.8 to about 0.9, 0.1to 5% by weight, calculated on the weight of said polyethyleneterephthalate, of a decomposing agent selected- References Cited by theExaminer UNITED STATES PATENTS 2,799,664 7/1957 2,897,042 7/ 1959* Heiks8130.1 2,938,811 5/1960 Hermes 117102 3,014,011 12/1961 Zoetbrood 2603,070,575 12/1962 Cramer 26047 FOREIGN PATENTS 728,550 4/1955 GreatBritain.

WILLIAM H. SHORT, Primary Examiner. LOUISE P. QUAST, Examiner.

Drewitt 260-75

1. A PROCESS FOR MANUFACTURING POLYETHYLENE TEREPHTHALATE FIBROUSSTRUCTURES HAVING IMPROVED WEARING PROPERTIES WHICH COMPRISES ADMIXINGPOLYETHYLENE TEREPHTHALATE HAVING A SPECIFIC VISCOSITY OF ABOUT 0.8 TOABOUT 0.9 WITH 0.1 TO 5% BY WEIGHT, CALCULATED ON THE WEIGHT OF SAIDPOLYETHYLENE TEREPHTHALATE, OF A DECOMPOSING AGENT SELECTED FROM THEGROUP CONSISTING OF DIMETHYL TEREPHTHALATE, DIMETHYL ISOPHTHALATE,DIGLYCOL TEREPHTHALATE AND DIGLYCOL ISOPHTHALATE, REACTING SAID MIXTURETO DECOMPOSE SAID POLYETHYLENE TEREPHTHALATE TO A SPECIFIC VISCOSITY OFABOUT 0.5 TO ABOUT 0.6, AND SPINNING SAID MIXTURE TO FORM SAID FIBROUSSTRUCTURES, SAID SPECIFIC VISCOSITY BEING DETERMINED BY MEASURING THEVISCOSITY OF A 1% SOLUTION OF SAID POLYETHYLENE TEREPHTHALATE IN AMIXTURE OF 60 PARTS PHENOL AND 40 PARTS TETRACHLORETHANE IN A CAPILLARYVISCOSIMETER AT 25*C.